I found The Immolation to be a very good spot to farm Aether Crystals ; this is how a run goes for me (im doing this on a high lvl DW ranged Sorcerer with high survivability) :
I tp to Deadman's , kill the aetherials on the way to the aetherfire , then pit-stop at the small area without aetherfire to wait for Mirror of Ere to come off cooldown , and by the time it does , i kill the manticores in that small area , sometimes resulting in manticore eyes ; after that , i clear out the whole Immolation area (including the Herald , which has surprisingly good drops on Ultimate in my opinion)
My best results from a single run were : 15-16 crystals (cant remember clearly) , 1 shard , 1 cluster , and also 2 dynamites which spawn at the end of the run , alongside 2 strongboxes / 1 small box and 1 heroic chest
the run doesnt take too much time , and is clearly less boring than a Warden's Lab run

Totally forgot about that area which is weird because I do it on all my characters for the quest and always think "This area is pretty rewarding." updating OP

Also @Valinov updated OP again for clarity on why you'd pick one frozen heart option over another.

a. weaker character: Blood Grove portal, immediately cross bridge and bee-line to Darkvale village boss. Very fast with any AoE and nets 1-5, usually 2+ each time.
b. tougher character and ultimate only: edge of reality run to chests. Usually nets 1 or 2. Also can net various others such as Bloods, etc.

-I start with your top path, then keep going clockwise around and down to Ancient Grove part 1. iirc Nets 1-8 ugdenbloom, depending on luck; usually 4-5. More from tree stumps than heroes. But this circuit can run into Bargoll(ugdenbloom drop) and the Wendigo boss on the way to Grove. You could cut it short at the Grove door, if trying for minimum time runs- for a general loss of 1-3 ugdenblooms.

4. Aether crystals/shards:

-Malmouth outskirts portal clockwise path to Shrine. Nets 8 crystals.

-crossing from Malmouth outskirts to Mourndale. Nets 5-6 crystals.

-Lazy vendor farming in Steelcap District nets 1 each time and potentially an aether shard.

For Dynamite I usually do Cronley -> Hanneffy Mine -> Staunton Mine.
There's a guaranteed spawn in the 2nd mine as well, and the boss there always drops a Scrap or a Dynamite himself.
Doing both mines and some other spots means you can find Fabius as well.
Always kick all the junk piles in these areas too: they have a decent chance of dropping a Dynamite. North and north-west from the Dynamite spawn in Cronley's are 2 spots where junk piles can spawn (where the wasps are), killing the wasps and hives there give Battered Shells and Serrated Spikes too.

Sometimes when I need multiple types of materials, I rotate between the Steelcap vendor and Isaiah in Homestead. Steelcap guy gives most of the stuff you need to craft Dynamite (and sells a variety of MIs), and Isaiah has some rare components but is mostly used to reset the Steelcap vendor.

For Ugdenblooms I do the Gloomwald Crossing Rift that has 2 stumps NE of the Rift, and 2 more not too far away (someone probably has a map of this), and the original run I made when AoM was new.
Nowadays I kill all the treants and the plants along the way as well, since they have a good chance of dropping a bloom.
If you run this area a lot, try to keep the Gloomwald Shrine unpurified, since it's a bunch of extra bosses every run.
Just kill the first wave of creatures and leave the rest and reset the game or go somewhere else.

You can do the above with the shrines in Bastion of Chaos and Ancient Grove as well, by the time you reach these shrines you should be capped on Devo points already so you don't need them for that.

__________________"They were completely unbalanced—in all the best ways!"

Been farming SoT for a while, now that my fresh char has Ugdenbloom-crafted components in most slots and he's strong enough not to die to Alkamos.
A tip I have is that the Solael Guardian is very close to the exit of SoT after you finish that run: you just have to walk a bit to the west and then north, so you can farm him as well with little time loss.
I finish the run up by selling at the Steelcap vendor, and buying his components and crystals.

Made an addition to my Ugdenbloom run as well: after hitting the 4-5 stumps in Gloomwald Crossing, I walk back north to the Den of Carraxus.
The chest just outside the cave usually has several treants popping up from the ground when you approach it, and inside the place you can often find a cluster of treants as well.
Sometimes you get 3-4 hero treants in one of those places, who usually drop a bloom each.

__________________"They were completely unbalanced—in all the best ways!"